Researchers Control Love-Hate Relationship Between Atoms
December 11, 2002

This graphic depiction shows a gas cloud of lithium-6 atoms after it was cooled and subjected to a magnetic field. The 'before' view shows that the cloud resembled a cigar shape just after it was released from the laser trap. Later on, the cloud has expanded dramatically in the perpendicular direction and assumed an elliptical shape.

Research that makes ultra-cold atoms extremely attractive to one another may help test current theories of how all matter behaves - a breakthrough that might lead to advanced transportation systems, more efficient energy sources and new tests of astrophysical theories.

The experiment was conducted by a team led by Dr. John Thomas, a physics professor at Duke University, Durham, N.C., under a grant from NASA's Biological and Physical Research Program through the Jet Propulsion Laboratory, Pasadena, Calif.

The team manipulated a type of interacting atoms that behaved like fermions -- sub-atomic particles that are the building blocks of all matter, but are difficult to study directly. Normally, these atoms, called fermionic atoms, avoid each other at all costs. In this case, the researchers confined and cooled a lithium-6 gas cloud of atoms, and then introduced a magnetic field that acted as a matchmaker, inducing the atoms to attract one another strongly.

"This newly-created cold atom system has universal properties," Thomas said. "Understanding the behavior of these oddly-interacting atoms could yield new energy sources by testing the theory of how particles smaller than atoms behave. The same type of experiment may also help us study both neutron stars and nuclear matter, which are difficult to study in nature." Neutron stars are extremely dense stars made mostly of uncharged atomic particles.

Thomas and his colleagues used a "bowl" made of laser light in a vacuum to confine lithium-6 atoms in a cigar-shaped cloud. They cooled the cloud nearly to absolute zero, the point at which scientists believe no further cooling can occur and the atoms move as slowly as permitted by the laws of quantum mechanics. Normally, when a gas cloud of any shape is released in a vacuum, it expands in all directions until it becomes a sphere. But when Thomas and his colleagues introduced a magnetic field, something much different happened.

"In this case, the lithium atoms played 'follow-the-leader' and expanded rapidly in a direction perpendicular to the cigar shape, until the gas cloud was shaped like a bulging disc," Thomas said. "It's the first time this type of behavior has been observed in a fermionic gas and is the result of strong interactions between the atoms."

It's possible the cold atoms used by his team were actually behaving like a new type of superconductor that could operate at very high temperatures, Thomas said. A superconductor is a quantum state in which electricity can flow without resistance. The current generation of superconductors, used most commonly to make powerful magnets, can function only at low temperatures.

The ultimate rail system would use cars levitated above the track by magnets, but because the currently available superconducting magnets require low temperatures, they are difficult to use. If scientists could develop a superconducting magnet that could operate efficiently at high temperatures, it would solve the cooling problem and enable us to develop advanced high-speed transportation systems.

Thomas pointed out that his team members are not certain they were observing a superconductor phenomenon in the gas cloud, and further research is needed to determine whether there could be a different explanation.

Thomas co-authored a paper on the research, which will appear in the Dec. 13 issue of the journal Science. The paper appears online at the Science Express website at http://www.sciencemag.org/cgi/content/abstract/1079107. The co-authors, all from Duke University include Dr. Ken O'Hara, and students Staci Hemmer, Michael Gehm and Stephen Granade.

Thomas' research was funded by NASA, the National Science Foundation, the Department of Energy and the Army Reserve Office. JPL manages the Fundamental Physics in Microgravity Research Program for NASA's Office of Biological and Physical Research, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.